The Study On Refractive Index Sensing Based On Fiber Structures Coated With Graphene

Optical fiber sensing technology has been applied to biochemistry,environmental monitoring,medical and other fields,due to its advantages of high sensitivity,small volume,anti electromagnetic interference,and so on during recent years.How to improve the refractive index sensitivity and eliminate the cross-influence of temperature are the hot research spots.In this dissertation,we have inverstigated two kinds of refractive index sensors based on novel hybrid waveguide structures: tilted fiber grating(TFBG)and hollow silica tube(HST)coated with the graphene.Firstly,the refractive index sensor based on graphene coated TFBG was investigated.The thickness of coated graphene on the fiber surface can be controlled by setting the growth time and the power of applied plasma.In the experiment,the used TFBG with a tilted angle of 8° was coated graphene with thickness of 3.7 nm(about 11 layers).Results show that the refractive index sensitivity of TFBG with graphene is-1.57161/RIU near 1.33,which is about 20 times of that of TFBG without graphene.Therefore,combining the TFBG with graphene can improve the sensitivity near the low refractive index.Secondly,another gas refractive index sensing device was investigated.Graphene with thickness of about 3.3 nm(about 10 layers)was coated on the surface of HST with length of 3 mm,which acts the sensing part of the refractive index and temperature.Analysising the optical signal intensity,the refractive index sensitivity of the graphene-HST hybrid waveguide structure is up to 418.23dB/RIU with a slight wavelength shift of 16.73pm/ RIU,which is several or even dozens of times than other reported results based on intensity modulation.Its temperature sensitivity is 17pm/?with a slight intensity change of 0.011dB/?.Compared with the refractive index sensitivity of 418.23dB/RIU,0.011 dB can be ignored.Thus,the graphene-HST hybrid waveguide structure can be applied to refractive index sensing without temperature-cross effect.